Principles of Inheritance and VariationNEET MCQs with solutions
Principles of Inheritance and Variation is one of NEET's heaviest chapters. Mendelian genetics, incomplete dominance, co-dominance, multiple allelism (blood groups), sex-linked inheritance, chromosomal disorders and pedigree analysis are all tested. Problem-solving questions dominate — practising crosses and ratios is more important than memorising definitions.
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- 12 Biology
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Q1Important PYQ Mixed Concepts
Experimental verification of the chromosomal theory of inheritance was demonstrated through the work of which scientist?
Not quite — the answer is B.
T.H. Morgan experimentally verified the chromosomal theory using Drosophila and demonstrated linkage and sex-linked inheritance. Sutton and Boveri proposed the chromosomal theory, whereas Mendel established the laws of inheritance.
Q2Important PYQ Mixed Concepts
In a Mendelian monohybrid cross, the separation of the two alleles of a gene during gamete formation represents which law?
Not quite — the answer is C.
The law of segregation states that the two alleles of a gene separate during gamete formation, so each gamete receives only one allele. Independent assortment concerns the segregation of alleles of different genes on different chromosomes. Dominance describes the masking of one allele by another, not gamete formation.
Q3Inheritance of One Gene
In a cross between pure tall (TT) and pure dwarf (tt) pea plants, the phenotype of all F1 progeny will be:
Not quite — the answer is C.
TT × tt produces all Tt offspring; T is completely dominant over t, so all F1 are tall. Intermediate phenotype would indicate incomplete dominance, which does not apply here.
Q4Inheritance of One Gene
A testcross to determine genotype of a dominant phenotype individual involves crossing with:
Not quite — the answer is D.
Testcross uses homozygous recessive (tt) so any recessive offspring unambiguously reveals a recessive allele in the tested parent. Crossing with dominant individuals cannot reveal hidden recessive alleles.
Q5Chromosomal Theory of Inheritance
The chromosomal theory of inheritance was proposed independently by:
Not quite — the answer is A.
Sutton and Boveri independently proposed that Mendelian factors (genes) are located on chromosomes, based on the parallel behaviour of chromosomes and hereditary units. Mendel-Morgan and Darwin-Wallace are incorrect pairings for this theory.
Q6Chromosomal Theory of Inheritance
The chromosomal theory of inheritance correlates chromosome behaviour during meiosis with:
Not quite — the answer is B.
Chromosome segregation and independent assortment during meiosis directly parallel Mendel's laws of segregation and independent assortment. Protein synthesis and DNA replication are unrelated to inheritance patterns.
Q7Mendel's Laws of Inheritance
In a heterozygous pea plant (Tt), only the tall phenotype is expressed. This demonstrates:
Not quite — the answer is A.
In Tt, the T allele masks expression of t, demonstrating Law of Dominance. Segregation relates to gamete separation; independent assortment involves non-linked gene pairs.
Q8Mendel's Laws of Inheritance
The Law of Segregation is also referred to as:
Not quite — the answer is B.
Alleles separate during gamete formation without blending or contaminating each other, hence called Law of Purity of Gametes. Blending inheritance was the pre-Mendelian incorrect view.
Q9Grand Test
A colour-blind man marries a woman who is homozygous for normal colour vision. What is the probability that their son will be colour-blind?
Not quite — the answer is A.
The father is XcY and the mother is XNXN. Every son receives Y from the father and XN from the mother, giving XNY genotype. Therefore none of the sons will be colour-blind. All daughters will be carriers.
Q10Grand Test
Mendel selected seven pairs of contrasting characters in pea plants. Which combination contains only characters actually studied by Mendel?
Not quite — the answer is D.
Mendel's seven characters included seed shape, seed colour, flower colour, pod shape, pod colour, flower position and stem height. Root length, leaf shape, flower scent and oil content were not among his selected pairs.
Q11Inheritance of Two Genes
In a dihybrid cross, the number of different gamete types produced by AaBb individual is:
Not quite — the answer is B.
Gamete types = 2ⁿ where n = number of heterozygous gene pairs; AaBb has n = 2, so 2² = 4 gametes (AB, Ab, aB, ab). Option C (8) applies to trihybrid AaBbCc individuals.
Q12Inheritance of Two Genes
In dihybrid cross AaBb × AaBb, the probability of obtaining genotype aabb is:
Not quite — the answer is C.
P(aa) = 1/4 and P(bb) = 1/4; by multiplication rule for independent genes: 1/4 × 1/4 = 1/16. Option A (1/8) is a common error from adding rather than multiplying probabilities.
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Get RankUp on Google PlayQ13Sex Determination
In humans, sex determination follows which chromosomal system?
Not quite — the answer is A.
Human males are XY and females are XX — this is the XX-XY system of sex determination.
Q14Sex Determination
Which parent determines the sex of offspring in humans?
Not quite — the answer is B.
The father produces X-bearing and Y-bearing sperms; the mother produces only X-bearing eggs. Hence the father determines offspring sex.
Q15Mutation
A sudden heritable change in genetic material is called:
Not quite — the answer is A.
Mutation is defined as a sudden heritable change in genetic material; unlike variation, it is specifically a change at the DNA sequence level.
Q16Mutation
The term 'mutation' was first coined by:
Not quite — the answer is B.
Hugo de Vries coined the term 'mutation' while studying discontinuous variations in Evening Primrose (Oenothera lamarckiana).
Q17Genetic Disorders
A genetic disorder caused by alteration in a single gene is called:
Not quite — the answer is A.
Mendelian disorders arise from mutation in a single gene and follow Mendelian inheritance patterns; chromosomal disorders involve changes in chromosome number or structure.
Q18Genetic Disorders
Which of the following is a Mendelian disorder?
Not quite — the answer is B.
Haemophilia is caused by mutation in a single X-linked gene; Down, Turner, and Klinefelter syndromes are chromosomal disorders caused by aneuploidy.
Q19Mixed Revision
A woman with blood group A has a child with blood group O. Which genotype must the woman possess?
Not quite — the answer is C.
An O-group child has genotype ii and must receive an i allele from each parent. Since the mother has phenotype A, her genotype must be IAi to carry the i allele. IAIA cannot produce an i-bearing gamete. IBi gives blood group B, not A. ii gives blood group O, not A.
Q20Mixed Revision
Which statement correctly explains why Mendel selected pea plants for his experiments?
Not quite — the answer is D.
Pea plants offered distinct contrasting characters, short generation time, large offspring numbers and easy controlled self- and cross-pollination. These features enabled Mendel to study inheritance systematically. The other options are factually incorrect for pea plants.
Q21Mendel's Laws of Inheritance
According to Mendel, allele pairs separate during:
Not quite — the answer is C.
Segregation of alleles occurs during gamete formation (meiosis), not fertilisation or mitosis. Fertilisation is when gametes fuse, not separate.
Q22Mendel's Laws of Inheritance
The Law of Independent Assortment applies when genes are located on:
Not quite — the answer is D.
Independent assortment operates only when genes are on non-homologous (different) chromosome pairs. Linked genes on same chromosome violate this law.
Q23Mendel's Laws of Inheritance
The phenotypic ratio in F2 generation of a monohybrid cross is:
Not quite — the answer is A.
Monohybrid cross (Tt × Tt) gives 3 tall : 1 dwarf in F2 phenotypic ratio. The 1:2:1 is genotypic, not phenotypic.
Q24Mendel's Laws of Inheritance
In F2 of a monohybrid cross, the genotypic ratio of homozygous dominant : heterozygous : homozygous recessive is:
Not quite — the answer is B.
Monohybrid F2 yields TT : Tt : tt = 1:2:1. The phenotypic 3:1 ratio groups TT and Tt together; genotypically they are distinct classes.
ELITE question · AIR under 50 level
This chapter has 288 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Ratios & Concepts
Quick revision: most questions in this chapter test these facts.
| Concept | Key Fact |
|---|---|
| Monohybrid ratio | 3:1 (F2 phenotypic); 1:2:1 (genotypic) |
| Dihybrid ratio | 9:3:3:1 (F2 phenotypic); independent assortment of non-linked genes |
| Incomplete dominance | F2 → 1:2:1 (e.g. snapdragon flower colour: red × white → pink) |
| Co-dominance | Both alleles express equally (e.g. ABO blood groups: I^A I^B → AB) |
| Sex-linked (X) | Colour blindness, haemophilia — more common in males (XY hemizygous) |
| Chromosomal disorders | Down (trisomy 21), Turner (45,X), Klinefelter (47,XXY) |
What the app covers in this chapter
593 questions in total, each with a detailed explanation.
| Important PYQ Mixed Concepts | 100 |
| Inheritance of One Gene | 80 |
| Chromosomal Theory of Inheritance | 80 |
| Mendel's Laws of Inheritance | 60 |
| Grand Test | 60 |
| Inheritance of Two Genes | 53 |
| Sex Determination | 40 |
| Mutation | 40 |
| Genetic Disorders | 40 |
| Mixed Revision | 40 |
Questions students ask
Is Principles of Inheritance important for NEET?
It is one of the most important and highest-weightage Biology chapters. NEET asks 3–5 questions every year from this chapter, including crosses, pedigree analysis, blood groups and chromosomal disorders.
Which topics should I revise first?
Master Mendelian ratios (3:1, 9:3:3:1), incomplete dominance and co-dominance, ABO blood group genetics, sex-linked inheritance patterns, and the three major chromosomal disorders (Down, Turner, Klinefelter).
How many questions from this chapter are on RankUp?
The RankUp app has 593 questions on Principles of Inheritance and Variation, including 288 ELITE questions written for students aiming at AIR under 50. Every question has a detailed explanation.
